Image display screen with fluorescence efficiency reducing coating



United States Patent 3 Claims. (Cl. 313-89) This invention relates toimage reproduction devices and to a method of forming screens for suchdevices.

Image display screens of the type adapted to be em ployed in colortelevision apparatus generally comprise a transparent viewing panelhaving a large number of discrete patterns formed thereon. Each patternmay consist of bars, dots or stripes of red, green and blue colorfluorescing materials. A screen of this type may be fabricated by aphotographic printing technique wherein a photosensitive material isused to bind the fluorescent material to the panel. In such a process,the transparent viewing panel is first coated with a thin film of aphotosensitive substance and a fluorescent material. The panel is thenexposed to light through an appropriate negative to cause thephotosensitive substance to harden and ad here to the panel. Thoseportions of the screen which are not exposed to light are subsequentlyremoved by dissolving the substance with a suitable solvent. Thisprocedure is repeated for each fluorescent material pattern used in thedisplay device to complete formation of the fluorescent screen.

An image display device of the type described above may use an aperturemask or grid which is positioned behind the screen for the purpose ofmasking, deflecting or focusing the electron beam or beams employed inthe device. The electrons are directed to pass through the mask or gridapertures to impinge upon the appropriate color fluorescing materialareas. During operation of the device, a given percentage of theelectrons in the beam strike the surfaces of the grid which define theapertures, and are deflected therefrom in random directions toward thescreen. In addition to these deflected primary electrons, a considerablenumber of secondary electrons are emitted from the mask or grid surfacesdue to bombardment by the primary electrons, some of which also proceedtoward the mask from random directions. Impingement upon the screen ofthese deflected primary and secondary emissive electrons, which have alower velocity than the directly impinging primary electrons,

tends to desaturate the reproduced color image. Such an eiiect is morenoticeable on a color field produced by a low efficiency colorfluorescing material such as one of the red phosphor materials, zincphosphate. In this instance, de-saturation occurs when the randomelectrons strike screen areas other than the desired areas, such asthose covered by green and blue phosphor materials, to cause dilution'otthe red field. Since it is the aim of television manufacturers toprovide cans for reproducing a color image having the same colorcharacteristics as the transmited image, any observable de-saturatlon ofone or more of the color fields is highly undesirable.

Accordingly, it is an object of the invention to reduce colorde-saturation in an image display device.

A further object is to improve the fabrication of image display screens.

The foregoing objects are achieved in one aspect of the invention by theprovision of an image display screen which utilizes the addition of afluorescent material or phosphor poisoning agent to reduce the surfaceefiiciencies of pre-selected ones of the fluorescent materials used toform the screen. The lower velocity electrons in the display device willnot penetrate into the poisoned phosphor crystals sufflciently far tocause excitation thereof. However, the high velocity primary electronswill penetrate the crystals to provide normal illumination. Byselectively lowering the surface efficiencies of the phosphors, areduction in color de-saturation can be achieved.

Briefly, the screen pattern may be produced by a photographic printingoperation wherein the viewing panel of the display device is coated witha light hardenable substance and an appropriate phosphor. Subsequently,this coating is exposed to light through a mask'or negative having thedesired bar, dot or stripe configuration. This exposure operation causesthe coating to harden and adhere to the viewing panel. The unexposedportions of the coating are then removed from the panel by washing witha suitable solvent for the light hardenable substance. The abovedescribed process may be repeated for each color fluorescing materialused in the screen, with proper olfsetting of the negative relative tothe light source during each exposure operation.

The phosphor poisoning agent may be applied to the phosphor materialbefore application in the screening process, or it may be introduced atsome stage in the process. For instance, the light hardenable materialmay serve as a carrier for the agent, or it may be applied as a separatestep after one or more of the fluorescent material patterns have beenformed to selectively lower one or more of the phosphor surfaceefficiencies. It has been found advantageous to heat the screen afterthis treatment to aid in the diffusion of the poisoning agent into thesurface of the phosphor crystals.

The fluorescent materials employed in the screen may be any type ofelectric field and/or electron-responsive inorganic material such asthose formed from sulfides, oxides, tungstates, aluminates, borates,selenides, phosphates or silicates of one or more metals included in thegroup of zinc, cadmium, beryllium, magnesium, manganese, calcium,strontium and others well known in the art. These materials may beactivated by such metals as silver, copper and manganese.

The photosensitive or light hardenable substance used in the process maycomprise any well known formulation which is rendered non-dispersible orsubstantially insoluble after being exposed to light. Among thematerials suitable for use in the production of image display screensare photographic gelatins, polyvinyl alcohol, polyvinyl pyrrolidone,polyvinyl acetate, etc. sensitized with such substances as ammonium,potassium or sodium dich-romates, monomeric type dye-sensitizedpolymers, and a variety of lacquers such as Kodak Photosensitive Lacquer(KPL) and Kodak Ph-otoresist (-KPR), which have incorporated therein avolatile sensitiz-er.

The solvent or developing fluid used to dissolve the unexposed portionsof the light hardenable material is dependent upon the particularphotosensitive substance employed. For instance, an organic solvent suchas trichlorethylene or a ket-one may be used with commercialphotosensitive lacqucrs and with polyvinyl acetate whereas othersubstances such as polyvinyl alcohol are soluble in water.

The phosphor poisoning agent employed in the process may include one ormore of the metals included in the group comprising iron, cobalt, ornickel. The application of these metals may be made in the form of asalt solution e.g. sulfates, chlorides, nitrates, etc. of the metals.

In detail, one process for forming image screens employing phosphorswith pre-selected surface efliciencies utilizes the application of awater solution of a light hardenable substance such as polyvinyl alcoholsensitized with ammonium dichromate to the transparent viewing panel toform a thin tacky coating thereover. A first fluorescent material suchas the green phosphor, zinc orthosilicate, which may be in powderedform, is then deposited upon the coating by a dusting operation. Thisphosphor adheres to the tacky surface of the sensitized polyvinylalcohol coating. If desired, the phosphor and sensitized alcohol may beapplied to the panel together in the form of a slurry. An aperture mask,grid or other type of appropriate pattern negative which Will producethe desired array of dots, bars or stripes is then positioned relativeto the coated panel to shadow those portions of the coating which areintermediate the desired green phosphor pattern configuration.Subsequently, the coated pane-l is exposed through the negative to lightemanating from a point source. The exposed portions of the polyvinylalcohol are hardened by the light and thereby adhere to the viewingpanel to provide a binding agent for the phosphor. The pattern isthereafter developed by Washing the panel with a suitable solvent suchas deionized water, which removes the unexposed portions of thepolyvinyl alcohol and phosphor.

In order to lower the surface efliciency of the zinc orthosilicatephosphor, the panel is then washed with a poisoning agent such as awater solution of ferric nitrate ranging in concentration from .1percent to .OGOOS percent by weight. The iron, or any of the otherpoisoning agents mentioned above, tend to decrease the surfaceefficiency of practically all of the known phosphors.

After the panel has been washed with ferric nitrate, it is again coatedwith a layer of polyvinyl alcohol anda blue fluorescing material such asZinc sulfide. The panel is then exposed to light through the negative toharden the coating in accordance with the form and position of thedesired blue phosphor pattern relative to the previously formed greenphosphor pattern. Ofifse-tting the light source and the negativerelative to one another during exposure provides proper displacement ofthese patterns. The 11 1- exposed portions of the coating are againremoved by application of a solvent such as deionized water, and theremaining coating is subsequently rinsed with the ferric nitratesolution to lower the efiiciency of the blue phosphor also.

The image display screen is completed with the application of polyvinylalcohol and a red color fluorescing material such as zinc phosphate,followed by exposure and development operations. During the exposureoperation, the light source and negative are again offset from oneanother so that a screen may be produced having a large number of triadsof green, blue and red color fluorescing dots, bars or stripes. Sincemost of the presently known red fluorescent materials have a lowerefliciency than the green or blue fluorescent materials, and since colordesaturation is more noticeable on the least eflicient color field, thered phosphor pattern is not subjecteclto the ferric nitrate treatment.Therefore, by using the process described above, the green and bluephosphor surface efiiciencies are reduced while the red phosphorefficiency is not altered.

Accordingly, during operation of the image display device, any lowvelocity electrons impinging upon the screen will not excite the greenand blue phosphors, and de-saturation of the red color field will beminimized. However, high velocity primary electrons will excite thegreen and blue phosphors in the normal manner so that there will be noloss in image brightness. Due to the relatively low efiiciency ofpresently available red, phos- 4 phors, any excitation thereof by lowvelocity electrons has practically no observable de-saturation effectson the other color fields.

The poisoning agent used in the process may be applied in a manner otherthan that which is described above. For instance, the phosphor crystalscan be coated with the agent prior to their application to the panel, orthe light hardenable material may have the iron, nickel or cobaltincorporated therein. It is to beunderstood that any screen whichutilizes selectively lowered surface efficiencies of one or morephosphors is contemplated as being within the scope of this invention,and that poisoning agents maybe applied to any or all of the phosphorsin concentrations sufiicient' to minimize color de-saturation.

As a final step in the screen forming process, the panel may be bakedabove 400 degrees centigrade to remove volatile impurities which existin the face panel and in the screen forming materials, and to aid in thediffusion of the ferric nitrate into the surface of the phosphorcrystals.

This application is a division of SN. 688,846, entitled Method ofFabricating Image Display Screens, filmed October 8, 1957 now U.S.Patent No. 2,996,380, and assigned to the same assignee as the presentinvention.

Althoughvseveral embodiments of the invention have been shown anddescribed, it Will be apparent to those skilled in the art that variouschanges and modifications may be made therein without departing from thescope of the invention as defined by the appended claims.

What is claimed is:

1. In an electron discharge device, a fluorescent image display screen,having reduced color de-saturation properties; bombarded by relativelyhigh velocity primary electrons and lower velocity secondary electronscomprising: a plurality of discrete areas of electron excitablefluorescent materials adjacently disposed in a repetitive patternrelative to one another to form said screen, each of said adjacent areascomprising a different phosphor, each having a given electron excitablelight output efiiciency level, at least one of said phosphors having a.fluorescent efliciency reducing salt coating forming a surface coveringlayer thereon to selectively lower the surface light output efficiencythereof and reduce said screen color desaturation upon bombardment bysaid lower velocity electrons, without substantially reducing thefluorescence efliciency of said phosphors under conditions ofbombardment by said high velocity electrons.

2. The structure of claim 1 wherein the salt is selected from the groupcomprising salts of iron, cobalt and nickel.

3. The structure of claim 1 wherein the phosphor having the lowestfluorescence efficiencyis free of the efficiency reducing salt coveringWhile the remaining phosphors are covered.

References Cited by theExaminer UNITED STATES PATENTS 2,862,130 11/58Sadowskyetal "313-925 2,937,150, 5/60 Lehmann 25230l.6

RALPH G. NIELSON, Primary Examiner.

ARTHUR GAUSS, Examiner.

1. IN AN ELECTRON DISCHARGE DEVICE, A FLUORESCENT IMAGE DISPLAY SCREEN, HAVING REDUCED COLOR DE-SATURATION PROPERTIES, BOMBARDED BY RELATIVELY HIGH VELOCITY PRIMARY ELECTRONS AND LOWER VELOCITY SECONDARY ELECTRONS COMPRISING: A PLURALITY OF DISCRETE AREAS OF ELECTRON EXCITABLE FLUORESCENT MATERIALS ADJACENTLY DISPOSED IN A REPETITIVE PATTERN RELATIVE TO ONE ANOTHER TO FORM SAID SCREEN, EACH OF SAID ADJACENT AREAS COMPRISING A DIFFERENT PHOSPHOR, EACH HAVING A GIVEN ELECTRON EXCITABLE LIGHT OUTPUT EFFICIENCY LEVEL, AT LEAST ONE OF SAID PHOSPHORS HAVING A FLUORESCENT EFFICIENCY REDUCING SALT COATING FORMING A SURFACE COVERING LAYER THEREON TO SELECTIVELY LOWER THE SURFACE LIGHT OUTPUT EFFICIENCY THEREOF AND REDUCE SAID SCREEN COLOR DESATURATION UPON BOMBARDMENT BY SAID LOWER VELOCITY ELECTRONS, WITHOUT SUBSTANTIALLY REDUCING THE FLUORESCENCE EFFICIENCY OF SAID PHOSPHORS UNDER CONDITIONS OF BOMBARDMENT BY SAID HIGH VELOCITY ELECTRONS. 